It worked out for me by editing the themes whichever you are using (day,dawn , dusk etc)
location: suitecrm-7.11.3-0\apps\suitecrm\htdocs\themes\SuiteP\css\Day\style.css - set visibility: hidden;
like below.
.sidebar .recentlyViewedSidebar {
margin-bottom: 12px;
float: left;
width: 100%;
visibility: hidden;